I'm having a hard shifting situation lately. Some times when I start the car the transmission warning light comes on and I will have the hard shifting situation. Anyone else had this happen or know anything that may help?

 

Hi danomite,

On our '93 the most common cause of the Limp Home Mode (LHM) with the transmission warning lamp illuminated has been oil contamination of the electrical connector for the Throttle Position Sensor (TPS). The connector is mounted on a bracket just to the left of the throttle body. You might check that connector and flush it with zero-residue electrical contact cleaner spray.

Also, check your transmission fluid to ensure that it is clear and red and comes exactly to the HOT line on the dipstick after a 15 minute drive. Park on a level surface and leave the engine running. Hold the brake pedal and move the gear selector lever to each position on the J-gate, pausing at each gear for 4 or 5 seconds so that gear fully engages. Return the lever to Park, and with the engine still running, check the fluid level. Fluid that is low or overfull or old and deteriorated could be part of the problem. The best fluid I have found for these transmissions is Redline Oil D4 ATF. It has the closest viscosity index to the original Dexron III that I have found and replacing Dexron VI with D4 transformed our transmission.

Beyond that, there are a number of possibilities. John Ping wrote an excellent diagnostic routine that you can find in the Jag-Lovers forum XJ40 eBook:

Jag-lovers' Ebooks

I also have some photos of various transmission components and how to service them:

Throttle Position Sensor (TPS):
Welcome to Jag-lovers - Members Photo Viewing Page

Transmission Electrical Connector:
Welcome to Jag-lovers - Members Photo Viewing Page

Rotary Switch:
Welcome to Jag-lovers - Members Photo Viewing Page

Decoder Module:
Welcome to Jag-lovers - Members Photo Viewing Page

Transmission Control Module (TCM):
Welcome to Jag-lovers - Members Photo Viewing Page

Cheers,

Don

 

I've personally had my TCM go into Limp Home Mode due to the Full Throttle Kickdown Switch under the accelerator pedal. The wires were strained (possibly from someone adjusting the switch--which spins--without disconnecting it first.) The wires were shorting and causes the hard shift and TCM light.

I was lucky enough to have a PDU to pull the TCM codes to lead me in the right direction. I'm not sure if there is a Short-and-Blink method (jumper pins on a diagnostic connector and count the flashes of the transmission light) for interrogating the TCM.

-Nick